PROCEEDINGS OF THE SOCIETY. 115 



problems were to be found in the intercrjstalline weakness of metal and 

 the so-called amorphous phase. 



A group of papers dealt with " Microscope Micrometry." 



Mr. Zay Jeffries (Cleveland, U.S.A.) communicated a paper on the 

 application of the microscope to the determination of grain size in 

 tungsten. 



Professor W. M. Thornton described a method of calibrating the 

 eyepiece micrometer of a microscope used for measuring small objects, 

 using a loose scale in the eyepiece in conjunction with a graduated slide 

 for calibration. 



Dr. A. E. H. TuTTON, F.R.S., contributed a paper on " The 

 Grayson Rulings." 



These wonderful rulings begin where others leave off, and they have 

 reached an extreme value of 120,000 to the inch, representing the 

 highest resolving power of the microscope. They are thus of great 

 value in studying resolution, while the rulings of 40,000 to the inch 

 (about the wave-length of red light) are capable of becoming of great 

 importance in metrology and as fiducial marks in connection with 

 interferometric fine-measurement in general. 



The recent death of Professor Grayson in Melbourne was a great 

 loss, and he hoped the meeting would help to ensure that his ruling 

 machine should be available for the continued production of rulings. 



A note by Professor H. Le Chatelier described and illustrated 

 " A Microscope used for Measuring Brinell Depressions." 



Dr. H. Hartridge, F.R.M.S., contributed a preliminary description 

 of "An Accurate Method of Objective-testing," and Mr. F. Twyman a 

 note on " The Testing of Objectives by Interferometry." 



Mr. Hartridge's method aims at being less dependent on the skill 

 of the observer than present methods. It consists in measuring with 

 a micrometer the position of the image pattern when different parts of 

 the objective aperture are used. If there is movement of the image 

 pattern the micrometer reading is plotted against the N.A. of the aper- 

 ture in use, and the resulting curve shows the aberrations present. 

 Examples of typical curves obtained are discussed. 



Mr. Twyman's method has not yet been much used, but actual tests 

 made show on an interference "contour map" aberrations of wave 

 surface not exceeding one wave length for monochromatic light. The 

 interferometer employed is briefly described. 



Lt.-Col. J. W. GiFFORD described how to make up simple " Light 

 Filters for the Microscope and Photomicrography." 



A solution of malachite green in glycerine is used which transmits 

 only a broad band in the region of the F line and a narrow red band, 

 and the latter is eliminated by the peacock-green glass used for making 

 the cells for holding the solution. For photomicrography a solution of 

 methyl violet is similarly used. The author's present method of making 

 the cells is described. 



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